WO1997035659A1

WO1997035659A1 - Process for conveying materials and device for implementing it

Info

Publication number: WO1997035659A1
Application number: PCT/EP1997/001181
Authority: WO
Inventors: Rudolf Jerkel
Original assignee: Wiwa Wilhelm Wagner Gmbh & Co. Kg
Priority date: 1996-03-22
Filing date: 1997-03-08
Publication date: 1997-10-02
Also published as: ATE265266T1; US6315442B1; JP2000507156A; EP0958040B1; KR20000004911A; US6161956A; DE59711584D1; EP0958040A1; DE19611339A1

Abstract

Instead of a discontinuous mixing process for mixing two or more materials for a paint-spraying plant, the invention proposes a continuous mixing and conveying process including the relevant device. To this end, use is made of individual conveyor pumps driven individually by hydraulic adjusting units in the form of double-acting hydraulic cylinders. Control is exerted by acting on hydraulic connecting lines between the adjusting units.

Description

Process for conveying materials and device for carrying out the process

Description:

The invention relates to a method for the synchronous delivery of flowable materials, each with a feed pump into a mixing device, from which the mixture of these materials can be supplied to a consumer, for example a paint spray gun, the feed pumps each using a hydraulic actuating unit can be actuated, in which an actuating piston is guided in an actuating cylinder, and the actuating units are located in a hydraulic circuit of a drive fluid acting on the actuating piston. The invention further relates to a device for performing such a method.

A method of this type and an associated device are already known from patent application EP 0 644 025 A1, in which two metering feed pumps convey the individual materials into a single mixing device in such a way that a drive element of a first feed pump applies a constant flow pressure and the flow pressure of the drive fluid acting on a second drive element is adjusted by control commands from a control device in such a way that the flow measurement values of the delivery flows generated by the feed pumps are in a predeterminable relationship to one another which can be applied to the control device as a setpoint.

While in the case of a relatively slow conveyance of the materials such a regulation actually ensures their homogeneous mixing, inhomogeneities in the conveyed mix can occur at relatively high conveying speeds, which are suitable for causing difficulties in technical application.

In addition, the functionality of the control essentially depends on pressure measurements and controls in the circuit of the drive fluid, which require calibratable and stable measuring instruments for the pressures that occur over a long period of time. The measured values from these pressure measurements must be linked to measured values for the distances covered by the actuating pistons, for the determination of which displacement sensors are attached to the actuating cylinders, which travel to and from the actuating pistons themselves or those connected to them Her¬ related components are controlled. The measured values of pressure and displacement are then to be linked with one another in order to obtain the actual values for the flow rates from the feed pumps and the current mixing ratio of the materials supplied to the mixer. Time delays are to be expected in particular for the generally mechanical measurement of the pressures. It is therefore not ensured that the materials are processed continuously to form a homogeneous mixture that always has the desired mixing ratio. Rather, local heterogeneity can sometimes be and avoid deviations from the mixing ratio.

It is also already known to carry out the conveyance of the materials by means of feed pumps, each of which is driven by a hydraulic actuating unit and in each of which the flow of the drive fluid effective in the actuating unit can be adjusted by a control valve which is controlled by a proportional controller becomes. Although high conveying pressures and outputs are easily managed here, the arrangement cannot often achieve uniform mixing in a wide conveying range to form a homogeneous mixture, because the actuating units cannot be synchronized with one another in such a way that the conveying directions are always in different actuating units agree and a reversal of the direction of the actuating piston movement takes place at the same time.

It is therefore obvious that the drive of several actuating units is carried out by only a single drive unit, so that the feed pumps are now operated simultaneously and a homogeneous distribution of the conveyed materials in the mixture is actually achieved. A prerequisite for proper functioning is a fixed and unchangeable mixing ratio. If you want to change the mixing ratio, however, the feed pumps must be changed. An additional, adjustable gear does not provide a remedy if the technical parameters are to be adhered to very precisely, without the need for complex tests to be carried out on the system beforehand. Such a transmission also represents a so-called swivel arm, with which a kinematic connection is occasionally established between the actuating pistons and which can be adjusted so that the ratio of the working strokes carried out with the actuating pistons can be changed; The (maximum) working stroke of one of the actuating units is usually left constant and the working stroke of the second actuating unit is changed. Here, too, the system must be reset after each change; To make matters worse, only limited drive and funding performance can be realized with such lever gears. The adjustment is associated with a considerable expenditure of time.

A method including an associated device is known from EP patent specification 0 116 879 B1, in which, instead of the pressure measurement values, the flow measurement values of the delivery flows are measured and applied as counter pulses of a control device and the delivery volumes of the materials involved are determined in this way, that a desired mixing ratio is approximated in a first mixer, the mixing block; the finished mixture is transported in batches to a second mixer, the mixing tube, from which it can then be continuously removed by a consumer. Accordingly, at least two mixers are required to produce a continuously conveyed mixture.

The object of the invention is therefore to design a method and an associated device of the type specified in the introduction in such a way that the materials are continuously mixed in a single mixing chamber and in a predeterminable mixing ratio, the size of which moves in an interval that meets all requirements; a homogeneous mixture is to be obtained. A simple, robust and inexpensive device should be operable with an inexpensive controller.

According to the invention, the object is first achieved by a method in which the actuating piston is driven back and forth by a drive motor on a first actuating unit and an essentially constant working volume of the drive fluid is provided in the hydraulic circuit, the strokes the actuating piston is measured in each case by displacement sensors arranged on the actuating cylinders, and the measurement signals obtained are fed into a regulating device for regulating a constant mixing ratio of the materials, and in the regulating device the difference between the respectively simultaneous measuring signals from two actuating units as the current actual value. The value is compared with an associated target value and a control signal for the mass flow of the drive fluid is formed by the second actuating unit from the difference between the actual value and the target value, and that the reversal points for the reciprocating movement of the actuating pistons with one another and with the Reversal point of the Be motion of the drive motor can be selected approximately simultaneously.

The control of the mixing ratios is greatly simplified by the invention, because now only the working strokes in the actuating units have to be measured, their relationship to one another by means of a constant working stroke of a first actuating unit and a variable working stroke defining the mixing ratio the second and each additional control unit is marked. Because, according to the invention, the movements of the actuating pistons run simultaneously and only the flow of the working fluid is regulated by the second and each further actuating unit, the speed of the actuating pistons changes in the subsequent actuating units. Proven displacement sensors are available for the displacement measurement of the piston strokes and are already used in such processes.

A device can be used for the method according to the invention, in which two actuating units are provided, are designed as double-acting hydraulic cylinders and are hydraulically connected to one another in such a way that the drive fluid conveyed from the first actuating unit under the influence of the drive motor drives the second actuating unit in the same direction. Accordingly, the first actuating unit acts as a drive both for a feed pump assigned to it for a first material and as a drive for the second actuating unit and thus for a second feed pump assigned to it for a further material, without the actuating units being mechanically connected to one another; the disadvantages of such a linkage described above are avoided here. A separate drive for each of the feed pumps has not been used in the device according to the invention. Their actuating units are hydraulically coupled to one another, and it is only necessary to ensure that the piston strokes run simultaneously on the second and possibly every further actuating unit with that on the first actuating unit, for which the prior art provides sufficient possibilities. As long as the drive fluid is not changed, this setting is made only once and must only be corrected if there are volume differences in the drive fluid due to leakage.

In the case of the double-acting hydraulic Actuators designed as cylinders can be easily connected hydraulically by alternately interconnecting the cylinder spaces of the actuating cylinders on both sides of the respective actuating piston by hydraulic connecting lines, which are best designed to be essentially non-lockable: the actuating pistons are opened this way always charged in the same direction.

The volume of the working fluid conveyed by the second actuating unit is influenced in that the connecting lines are connected to one another by a hydraulic control line and a controllable shut-off device is provided in the control line, the branches of the control line being preferably connected to one another in a hydraulic bridge circuit of the type Wheatstone bridge are linked and the shut-off device is arranged in the bridge branch of the bridge circuit; the shut-off device is expediently controllable by a proportional controller as a function of the control signal from the control device. Leakages are compensated for and a buffer for quantity differences is created during the regulation if a preferably non-lockable pressure accumulator for excess drive fluid is provided in the control line.

The reversal points of the reciprocating actuating pistons can be brought into agreement if the position of the actuating piston can be changed on at least one actuating unit when the drive fluid is present.

The design of the drive motor is fundamentally not dependent on the device according to the invention. However, it has proven to be particularly advantageous provides to operate it with compressed air. It is thus possible for it to be switchable as a function of the pressure difference between the connecting lines, for example of a directional valve placed in the pneumatic fluid lines for the drive motor, which in turn can be switched by the pressure difference; in this way, the drive motor can only be activated when the hydraulic system is in operation. In its reversal points, the reversal of direction can be controlled by touch switches or the like. The use of compressed air as drive energy is particularly advantageous (explosion protection) if the method according to the invention is used in paint spraying.

It is expedient if a drive piston of the drive motor, the actuating piston of the first actuating unit and a metering piston of the feed pump belonging to this are rigidly connected to one another, preferably by means of fixed couplings between the respective piston rods.

The control of the drive fluid can take place with a control block of four check valves installed in the control line, which are switched so that the drive fluid from one connection line in the event of overpressure against the other connection line via the shut-off device into the pressure accumulator or into the other Connection line, with negative pressure against the other connection line, however, is fed from the pressure accumulator or from the outlet of the shut-off device. For this purpose, the control line can consist in each case of one branch for the connecting lines, and one check valve can be provided in each branch for both flow directions, with the check valves being connected a common feed or discharge line for the shut-off valve is connected in the same flow direction; the pressure accumulator can be connected to the common line by a branch.

Such a simple arrangement ensures the control of the second actuator with very simple means. The control elements here are tried and tested components of simple design with a long service life, which can also be quickly replaced in the event of a defect.

It is readily possible for the actuating unit to be flanged to the drive motor in a known manner by means of a plurality of spacer bolts so that a moving machine part remains visible between the pistons of the drive motor and the actuating unit. This machine part can be equipped with a position transducer which is stationary on it and which triggers measurement signals in a displacement sensor which is stationary on the drive motor and / or the actuating unit; such an arrangement can also be provided between the actuating unit and the flange-mounted feed pump. It is very economical if an incremental length measuring rod is used as the displacement sensor. Such transducers consisting of a displacement sensor and a displacement sensor are commercially available in many dimensions and with adjustable measuring lengths.

Overall, the invention has made it possible for the mixture removed by the consumer from the mixer not only to be largely homogeneous, but also to be supplied in a constant ratio of the material proportions. At the same time, expensive special constructions for the structural and functional elements used are avoided and instead, construction components that have long been commercially available are parts used.

The invention is explained in more detail below with the aid of an exemplary embodiment. The single figure shows a device according to the invention in a highly schematic representation, with which the method according to the invention can be carried out particularly advantageously.

A device according to the invention essentially consists of a pneumatic drive motor 1, a first hydraulic control unit 2 flanged to the drive motor 1, a second hydraulic control unit 3 which is driven by the first control unit 2, and the associated lines and Control devices.

The actuators 2,3 are two for driving the pumps 4 För ^¬ for metered delivery per a flowable material in a non-visible in the drawing Misch¬ device, in particular in a static mixer or dynami¬ rule conventional design, the pen with the Förderpum¬ 4 can be connected via the outputs 41a, 42a by hoses or pipes.

The actuating units 2, 3 are essentially composed of one actuating cylinder 21, 31 and one actuating piston 22, 32, piston rods 23, 33 being provided for the actuating pistons 22, 32, which guide the actuating pistons 22, 32 serve in the actuating cylinders 21, 31. The piston rod 23 also drives the actuating piston 22; For this purpose, it is connected to a piston rod 12 belonging to a drive piston 11 with the aid of a fixed coupling K. The drive piston 11 is part of the pneumatic drive motor 1, which as double-acting piston engine is formed. However, the corresponding compressed air lines ending in its piston cylinder 13 have been omitted in the drawing; they are not directly part of the invention and are customary in the art. In one of these lines, a pneumatic directional control valve can be arranged, which only allows the drive motor 1 to be switched as a function of the correct switching of the hydraulic range.

The actuating units 2, 3 are designed in the same way as the drive motor 1; their respective cylinder spaces Z2, Z3 or Z2 ', Z3' in the actuating cylinders 21, 31 in front of and behind the actuating pistons 22, 32 are hydraulically connected to one another by connecting lines 5. A first connecting line 51 links a cylinder space Z2 of the actuating unit 2 with a cylinder space Z3 'of the actuating unit 3 and a second connecting line 52 connects the two other cylinder spaces Z2', Z3 with one another. When the drive piston 11 is driving in the conveying direction, the plunger pressure exerted by the drive piston 11 prevails in the cylinder spaces Z2.Z3 ', while the other cylinder spaces Z2', Z3 have a significantly lower hydraulic pressure because the actuating pistons 22, 32 there only the pure displacement work has to be done on the drive fluid. During the counter stroke of the drive piston 11, the pressure conditions are reversed accordingly.

Branches 61a, 61b of a control line 61 are branched off from the connecting lines 5 at a control device 6, which also comprises a shut-off device 63, a control block 64 and a pressure accumulator 65. An electronic control device 66 controls the shut-off device 63. The shut-off device 63 is moved by a proportional controller 63a in such a way that a second feed pump 42 flanged to and driven by the actuating unit 3 feeds a feed volume which can be changed compared to a first feed pump 41 into the mixer. For this purpose, the volume flow moved by the respective connecting line 5 from the actuating piston 22 is split up by the shut-off device 63 into a portion which is fed into a cylinder space Z3, Z3 'of the second actuating unit 3 and which does not fit the shut-off device 63 at all ¬ siert, and in a portion that is returned via the other connecting line 5 into the actuating unit 2 and also into one of its cylinder spaces Z2, Z2 '.

In this way, the actuating unit 2 is used to a certain extent as a control unit with a constant working stroke and constant flow from the flanged-on feed pump 41, while the actuating unit 3 as a follower executes a variable working stroke that delivers the flow from the second feed pump 42 and determines the respective mixing ratio of the materials fed to the mixer.

The branches 61a, 61b of the control line 61 form a hydraulic bridge circuit B in the manner of a Wheatstone bridge, in the bridge branch 60 of which the shut-off device 63 is placed. The control flow flowing through the bridge branch 60 directs its flow direction according to the conveying direction of the drive piston 11, the opposite direction being blocked by check valves R. The blocking direction of two strands of control line 61 converging at a common end E1, E2 of bridge branch 60 is the same in each case. The pressure accumulator 65 is also connected to the bridge branch 60, into which excess working fluid, which may flow out of the pressure accumulator 65 if necessary, is fed.

The adjustment paths of the actuating pistons 22, 32 in the adjustment units 2, 3 are detected by displacement sensors 66 a, 66 b, which are part of the control unit 66 and whose measurement signals are available as actual values in the control unit 66. The respective actuating piston 22, 32 itself can serve as a displacement transducer; however, it is also possible to use a separate displacement sensor attached to the piston rods 23, 33.

The control signal obtained by comparing the measurement signals supplied from the displacement sensors 66a, 66b with a changeable setpoint set on the control 66 is directly applied to the proportional controller 63a from the control.

Reference number ^

I drive motor

II drive piston

12 piston rod

13 piston cylinder 2 (first) actuator

21 actuating cylinders

22 actuating pistons

23 piston rod

3 (second) actuator 31 actuator

32 setting pistons

33 piston rod

4 feed pump

41 (first) feed pump 41a output

42 (second) feed pump 42a output

5 connecting line

51 (first) connection line 52 (second) connection line

6 control device

60 bridge branch

61 control line 61a, 61b branch 63 shut-off device

63a proportional controller

64 control block

65 pressure accumulators

66 Control device 66a, 66b displacement sensor

B bridge circuit

E1, E2 end

K fixed coupling R check valve

Z2, Z2 'cylinder space in the first actuator

Z3, Z3 'cylinder space in the second actuator

Claims

Expectations:

1. A method for the continuous, synchronous delivery of flowable materials, each with a feed pump (4) into a mixing device, from which the mixture of these materials can be fed to a consumer, for example a paint spray gun, the feed pumps (4) in each case can be actuated by means of a hydraulic actuating unit (2, 3), in which an actuating piston (22, 32) is guided in an actuating cylinder (21, 31), and the actuating units (2, 3) in a hydraulic circuit the actuating fluids acting on the actuating pistons (22, 32) are located,

characterized in that

(a) the actuating piston (22) is driven back and forth by a drive motor (1) on a first actuating unit (2),

(b) an essentially constant working volume of the drive fluid is provided in the hydraulic circuit,

(c) the strokes of the actuating pistons (22, 32) are each measured by displacement sensors (66a, 66b) arranged on the actuating cylinders (21, 31) and the measurement signals obtained in a control device (66) for regulating a constant mixing ratio. ratio of the materials are fed in,

(d) in the control device (66) the difference of respectively simultaneous measurement signals from two adjusting units (2, 3) as Compare the current actual value with an associated target value and

(e) an actuating signal for the mass flow of the drive fluid is formed by the second actuating unit (3) from the difference between the actual value and the desired value and

(f) the reversal points for the reciprocating movement of the actuating pistons (22, 32) with one another and with the reversal point of the movement of the drive motor (1) are selected approximately simultaneously.

2. Device for carrying out a method according to claim 1, characterized in that two actuating units (2, 3) are provided, designed as double-acting hydraulic cylinders and are hydraulically connected to one another in such a way that this is done under the influence of the drive motor (1) the first actuating unit (2) supplied drive fluid drives the second actuating unit (3) in the same direction.

3. Apparatus according to claim 2, characterized in that the cylinder spaces (Z2, Z2 '; Z3, Z3') of the actuating cylinder (21,31) on both sides of the respective actuating piston (22,32) are alternately connected to one another by hydraulic connecting lines (5) .

4. The device according to claim 3, characterized in that the connecting lines (5) are essentially not lockable.

5. Apparatus according to claim 3 or 4, characterized ge indicates that the connecting lines (5) are connected to one another by a hydraulic control line (61) and a controllable shut-off device (63) is provided in the control line (61).

6. The device according to claim 5, characterized_ in that the branches (61a, 61b) of the control line (61) are linked together in a hydraulic bridge circuit (B) in the manner of a Wheatstone bridge and the shut-off device (63) is arranged in the bridge branch (60) of the bridge circuit (B).

7. The device according to claim 5 or 6, characterized in that the shut-off device (63) by one

Proportional controller (63a) is controlled as a function of the control signal from the control device (66).

8. Device according to one of claims 5 to 7, characterized in that in the control line (61) a preferably non-lockable pressure accumulator (65) for excess drive fluid is provided.

9. Device according to one of claims 2 to 8, characterized in that on at least one actuating unit (3) the position of the actuating piston (32) can be changed when the drive fluid is present.

10. Device according to one of claims 2 to 9, characterized in that the drive motor (1) is operated by means of compressed air.

11. The device according to claim 10, characterized in that the drive motor (1) is switchable as a function of the pressure difference prevailing between the connecting lines (5).

12. The apparatus according to claim 11, characterized in that a directional valve is placed in the pneumatic fluid lines for the Antriebsmo¬ tor (1), which is switchable from the Druckdiffer¬ limit.

13. The device according to one of claims 2 to 12, characterized in that a drive piston (11) of the drive motor (1), the actuating piston (22) of the first actuating unit (2) and a metering piston of the feed pump (41) belonging to this are interconnected, preferably by means of fixed couplings (K) between the respective piston rods (12).

14. Device according to one of claims 2 to 13, characterized in that in the control line (61) a Steuer¬ block (64) of four check valves (R) is installed, which are switched so that the drive fluid from a connecting line (51 ) with overpressure against the respective other connecting line (52) via the shut-off device (63) into the pressure accumulator (65) or into the respective other connecting line (52), with negative pressure against the respective other connecting line (52), however, from the pressure storage rather (65) or from the outlet of the shut-off device (63).

15. The apparatus according to claim 14, characterized in that the control line (61) consist of one branch (61a, 61b) for the connecting lines (5) and in each branch (61a, 61b) each have a check valve (R) for both flow ¬ directions is provided, a common supply or discharge line for the shut-off device (63) being connected to the check valves (R) of the same flow direction.

16. The apparatus according to claim 15, characterized geke_ηnz_e_ichnet that the pressure accumulator (65) is connected by a branch to the common derivation.